1. Field of the Invention
The present invention relates generally to analytical reagent test strips for assaying fluid samples. More specifically, the reagent test strip of this invention is directed to a self-indicating format which provides accurate and reliable visual results without the need for an instrument or color chart.
2. Discussion of the Prior Art
Reagent test strips in general have been known for some time and are widely used in the health care industry. Such devices are called test "strips," because they typically comprise long, narrow sections of plastic or paper used both as a handle and as a support for a carrier matrix located at one end. The carrier matrix is generally a small paper-like pad which is incorporated with a reagent system.
When using a reagent test strip, the matrix is usually contacted with an analytical sample. The matrix is typically designed to take up the analytical sample by capillary action, and the sample thereby contacts and interacts with the reagent system of the matrix. The reagent system is typically designed to provide a color response in proportion to the amount of a particular analyte in the sample.
To determine the test strip's color change, the strip is generally either placed in an instrument, such as a reflectance photometer, or is compared with a color chart. However, instruments which read color are often expensive, may have reliability problems, and may require complex maintenance and operation by a skilled technician.
Color charts may fade due to sunlight or other ambient conditions or perhaps just due to time. Color charts may be expensive to manufacture and may be inconvenient for an operator to handle, particularly if the reagent strip and the color chart are to be handled together. Furthermore, persons with color perception problems may not be able to interpret a color chart properly. Moreover, a color chart standardized in a laboratory may not be accurate in the field where nonlaboratory conditions might alter test strip's color change, providing a color change that would not occur under laboratory conditions.
U.S. Pat. No. 4,042,329 by Hochstrasser is directed to a device for detecting cholesterol having a self-indicating format. In Hochstrasser, different reagent systems are incorporated into different "zones" of a bibulous, absorbent support material, such as paper. However, keeping each reagent separate during the incorporation process can be difficult, because as each reagent system moves into the absorbent carrier, it will continue to migrate throughout the carrier until it "dries", i.e., until substantially all of the solvent evaporates out of the reagent solution. In such a system, drying is a function of time, temperature, convection currents, substrate composition, solution composition and solution volume.
With so many parameters to control, such a method for reagent incorporation is prone to error. Furthermore, once the support is wetted with a sample, the reagent systems will once again be able to migrate and perhaps interact with one another. Hochstrasser suggests adding a nonabsorbent cover to the carrier with appropriately spaced apertures, thereby hiding areas between the reagent systems from a user of the system; this may cover up and help reduce the adverse effect of the migration problem, but certainly does not solve it. Also, applying different reagent systems to discrete zones of a support is a complex task that is not well suited for large scale manufacturing.
U.S. Pat. No. 4,046,514 to Johnston et al. is directed to a reagent strip with a self-indicating format. However, the Johnston device requires an interweaving of reagent threads and also requires that the resulting woven material be affixed to a support. However, weaving reagent threads is a complex process and affixing woven material to a support member can also be a cumbersome process which is not well suited to large scale manufacturing. The reagents in the interwoven threads can be prone to interact with one another, perhaps causing unwanted side reactions. Also, the adhesive which adheres the woven threads to the support adds to the system's complexity and may not be reliable or may interfere with the system.
Consequently, it is an object of the present invention to provide a self-indicating reagent test strip which is reliable, easy to manufacture, and can be accurately read by persons without the need for special technical skill or training and without the need for an analytical instrument or color chart.
A further object of the present invention is to provide a reagent test strip which will provide an accurate reading notwithstanding adverse environmental influences.
Other objects and features of the present invention will become apparent to those skilled in the art after reviewing the following specification.